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Abstract:

A lens assembling method for assembling a first lens and a second lens
where the first lens has a first mark on a first surface thereof and a
second mark on a second surface opposite to the first surface, and the
second lens has a third mark on a first surface thereof, the lens
assembling method including: a first step of aligning a position of one
of the first mark and second marks of the first lens with a position of
the third mark of the second lens; and a second step of aligning a
position of the other one of the first and second marks of the first lens
with the position of the third mark of the second lens, while keeping the
position alignment performed in the first step.

Claims:

1. A lens assembling method for assembling a first lens and a second lens
where the first lens has a first mark on a first surface thereof and a
second mark on a second surface opposite to the first surface, and the
second lens has a third mark on a first surface thereof, the lens
assembling method comprising: a first step of aligning a position of one
of the first mark and second marks of the first lens with a position of
the third mark of the second lens; and a second step of aligning a
position of the other one of the first and second marks of the first lens
with the position of the third mark of the second lens, while keeping the
position alignment performed in the first step.

2. The lens assembling method of claim 1, wherein the second mark of the
first lens and the third mark of the second lens are provided so as to
face each other, and in the first step, the position of the second mark
is aligned with the position of the third mark.

3. A lens assembling method for assembling a first lens and a second lens
where the first lens has a first mark on a first surface thereof and a
second mark on a second surface opposite to the first surface, and the
second lens has a third mark on a first surface thereof, the lens
assembling method comprising: a first step of aligning a position of one
of the first mark and second marks of the first lens with a position of
the third mark of the second lens; and a second step of aligning a
position of the other one of the first and second marks of the first lens
with the position of the third mark of the second lens, while keeping the
position alignment performed in the first step, wherein at least one of
the first step and the second step is a step of extrapolating a first
virtual mark or a second virtual mark respectively based on the first
mark or the second mark, and aligning a position of the first virtual
mark or the second virtual mark with the position of the third mark.

4. The lens assembling method of claim 3, wherein at least one of the
first mark and the second mark comprises multiple marks provided in an
outer peripheral area on a periphery of effective optical surface of the
first lens, wherein in the first step or the second step, with respect to
the multiple marks, a position of the virtual mark is extrapolated based
on the multiple marks provided in the outer peripheral area, and the
position of the virtual mark is aligned with the position of the third
mark.

5. The lens assembling method of claim 4, wherein the multiple marks,
provided in the outer peripheral area, of the first or the second mark,
are respectively provided at a same distance from an optical axis of the
first lens, wherein in the first step or the second step, with respect to
the multiple marks provided in the outer peripheral area, a weighted
center position of an area enclosed by the multiple marks is extrapolated
as the virtual mark, and the position of the virtual mark is aligned with
the position of the third mark.

6. The lens assembling method of claim 4, wherein positions of the
multiple marks of the first mark provided in the outer peripheral area,
and positions of the multiple marks of the second mark provided in the
outer peripheral area are arranged to be dislocated from each other.

7. The lens assembling method of claim 3, wherein at least one of the
first mark and the second mark is a circular mark centered with an
optical axis of the first lens, provided in an outer peripheral area on a
periphery of effective optical surface of the first lens, wherein in the
first step or the second step, with respect to the mark provided in the
outer peripheral area, a weighted center position of an area enclosed by
the circular mark is extrapolated as the virtual mark, and the
extrapolated position of the virtual mark is aligned with the position of
the third mark.

8. The lens assembling method of claim 7, wherein the circular mark of
the first mark provided in the outer peripheral area and the circular
mark of the second mark provided in the outer peripheral area have
different diameters from each other.

9. The lens assembling method of claim 1, wherein the first or second
mark which is provided in the effective optical surface of the first
lens, is provided on the light axis of the first lens.

10. The lens assembling method of claim 1, wherein the third mark is
provided on the light axis of the second lens.

11. The lens assembling method of claim 1, wherein the third mark
comprises multiple marks provided in an outer peripheral area on a
periphery of effective optical surface of the second lens, wherein in the
first step or the second step, a positions of a virtual mark, with
respect to the third mark, is extrapolated based on the multiple marks of
the third mark provided in the outer peripheral area, and the position
aligning is executed using the position of the virtual mark as the
position of the third mark.

12. The lens assembling method of claim 11, wherein the multiple marks of
the third mark are respectively arranged at positions of same distance
from an optical axis of the second lens, wherein in the first step or the
second step, a weighted center position of an area enclosed by the
multiple marks of the third mark is extrapolated as a position of a
virtual mark of the third mark, and the position aligning is executed
using the position of the virtual mark as the position of the third mark.

13. The lens assembling method of claim 1, wherein the third mark is, a
circular mark centered with an optical axis of the second lens, provided
in an outer peripheral area on an periphery of an effective optical
surface of the second lens, wherein in the first step or the second step,
a weighted center position of an area enclosed by the circular mark of
the third mark is extrapolated as a position of a virtual mark of the
third mark, and the position aligning is executed using the position of
the virtual mark as the position of the third mark.

14. The lens assembling method of claim 1, wherein the first mark and the
second mark are respectively provided on an optical axis of the first
lens, and the third mark is provided on an optical axis of the second
lens.

15. The lens assembling method of claim 1, wherein sizes of the first
mark, second mark and the third mark are respectively different from each
other.

16. A lens assembly comprising: a first lens provided with a first mark
on a first surface thereof, and a second mark on a second surface
opposite to the first surface; and a second lens provided with a third
mark, wherein the lens assembly is assembled in conditions that a
position of the second mark and a position of the third mark are aligned
to be matched with each other, and a position of the first mark and the
position of the third mark are aligned to be matched with each other.

17. The lens assembly of claim 16, wherein the second lens is provided
with a fourth mark on an opposite side surface to the surface formed with
the third mark.

18. An image capturing device comprising: the lens assembly described in
claim 16; and an image capturing sensor, which receives incident light
having passed through the first and second lenses, provided at an
opposite surface side, with respect to the second lens, to a surface side
where the first lens is arranged.

19. An image capturing device comprising: the lens assembly described in
claim 17; and an image capturing sensor, which receives incident light
having passed through the first and second lenses, provided at an
opposite surface side, with respect to the second lens, to a surface side
where the first lens is arranged.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a lens assembling method for
assembling a plurality of lenses to be provided in an optical device, an
assembly assembled with the plurality of lenses, and an image capturing
device provided with the lens assembly.

BACKGROUND TECHNOLOGY

[0002] Usually an optical system such as a digital camera and a mobile
phone with camera is structured with a combination of the plurality of
lenses. In cases of assembling these optical systems, by precisely
matching optical axes of the plurality of lenses with each other,
structuring the lens assembly by fixing between the lenses in matched
state, after that, the image capturing device is structured by arranging
an image capturing sensor on the lens assembly. In this case, the optical
system with displaced optical axes causes the problems of image
distortion, blurred image and the like, which cannot cause a good imaging
performance. For example, with respect to a camera lens unit including
the plurality of lenses it is required to assemble the plurality of
lenses in high precision, as image sensors being developed to be higher
density of pixels, and the assembling process is becoming difficult. For
example, in the work of assembling the plurality of lenses, an axis
aligning work to match the axis of each of the lenses is included, and to
precisely match each axis of the lenses by the aligning work is a work of
very high difficulty level. As the method of assembling the plurality of
lenses, there are mainly four types of assembling methods as shown below.
Said four types of assembling methods will be described referring to
FIGS. 14a-14d, which are section views of the lens showing the assembling
methods relating to the conventional methods.

[0003] A first method is a lens frame fitting assembling method. This is a
method of, as shown in FIG. 14a, tucking the side surfaces of first lens
500 and second lens 51 in lens frame 520, and assembling by physically
positioning the two lenses at the reference position of lens frame 520.
Since the positioning is executed by lens frame 520, the two lenses can
be easily assembled without executing the aligning work to match the
light axes of first lens 500 and second lens 510. However, since the
positioning of two lenses is conducted by the use of separate other part
such as lens frame 520, the problem of inferior positioning precision is
caused.

[0004] A second method is a reference position fitting assembling method.
In this method, as shown in FIG. 14b, flange 531 is provided in outer
circumferential area outside of an effective optical surface of the first
lens 530. Similarly, flange 541 is provided in outer circumferential area
outside of an effective optical surface of the second lens 540. Then, by
fitting the first lens 530 and the second lens 540, flanges 531 and 541
function as reference positions and the physical positioning of the two
lenses is performed to enable the assembling of the two lenses. According
to the second method, since the positioning of the two lenses is
physically executed with flanges (reference position), high precision
assembling can be easily performed without executing the aligning work to
align the light axes. Since the flanges function as the reference
positions, the positions of the flanges need to be precisely provided on
each lens, however high precision formation of the flanges is very
difficult. Namely, producing the lens having high precision reference
position is a work of high difficulty level. Further, conducting the
assembling work with measuring the reference position (flange position)
is also very difficult.

[0005] As a third method, there is a method of assembling lenses while
aligning the light axes by measuring the optical performance of the
lenses. For example, as shown in FIG. 14c, by providing the first lens
550 on the second lens 560 to form a lens assemble, the aligning is
performed by moving the first lens 550 in parallel direction (arrow
direction) while measuring the optical performance of the lens assembly.
Then, by determining the position where optical performance of the lens
assembly becomes good, the first lens 550 and the second lens 560 are
fixed. According to this assembling method, although the assembling can
be performed with high precision, a problem is caused that long time is
required for the axes aligning work including the measuring of the
optical performance. Further, this assembling method is only applicable
to the case of assembling the lens assembly that can be measured of
optical performance, which causes a problem of lacking versatility. For
example, in the case of assembling a lens unit having plural lenses,
since this method can be utilized only for the case of assembling the
last lens, this method lacks versatility.

[0006] As a forth method, there is a method of assembling lenses while
aligning the light axes by utilizing the mark formed on the lens. For
example, as shown in FIG. 14d, by providing mark 571 on the first lens
570 at the surface facing to the second lens 580, and providing mark 581
on the second lens 580 at the surface facing to the first lens 570,
reading the mark position of each lens, and matching the position of mark
571 with the position of mark 581 by moving the first lens 570 in
parallel direction (arrow direction), the axis aligning of the first lens
and the second lens is executed. By utilizing the marks in this way, the
axis aligning can be easily executed, however since this alignment is
only for the parallel direction, to precisely align the light axis is
difficult.

[0007] Namely, since the alignment is only for the parallel direction,
tilt is generated between the first lens 570 and the second lens 571.
According to the conventional method, the alignment is performed only in
the parallel direction, and the tilt cannot be adjusted. With respect to
the tilt, explanation will be done by referring to FIG. 15. FIG. 15 is a
section view of a lens assembly relating to the conventional technology.
According to the above described forth method, since the adjustment is
done only for the parallel direction of the lens, the tilt of axis having
tilt angle φ is generated between the first lens 570 and the second
lens 580, and this angle φ cannot be adjusted. According to the
method of conventional technology, for example, the tilted axis of 5-10
arc minutes (5'-10') is generated, which cannot satisfy the tilt angle
required for an optical system of 12 million pixels class, for example.

[0008] Further, a method of assembling lenses by forming a mark at an
outer peripheral area outside the effective optical surface of lens and
utilizing the mark is known (for example, Patent Document 1). A method of
assembling lenses by utilizing a deficiency existing at a prescribed
position in the effective optical surface of the lens as a mark for
positioning is known (for example, Patent Document 2). Further, a method
of executing the lens alignment by forming a mark on the lens is known
(for example, Patent Document 3).

[0012] However, according to the assembling method relating to the
conventional technology, it is difficult to adjust the tilt between
plural lenses, and the tilt angle required for an optical system of large
amount of pixels cannot be satisfied. For example, in the assembling
method described in Patent Document 1, it is difficult to perform the
alignment including the adjustment of the tilt between plural lenses.
Further, since the lenses described in Patent Document 2 and 3 are aiming
at an improvement of precision in eccentricity with respect to a lens
itself, it is difficult to adjust the tilt between plural lenses.

[0013] The present invention is for solving the abovementioned problems,
and aiming to provide a lens assembling method capable of assemble plural
lenses, in case of assembling the plural lenses, by adjusting the tilt
between the plural lenses. The present invention further aims to provide
a lens assembly assembled and adjusted with the tilt between the plural
lenses, and to provide an image capturing device including the lens
assembly.

Means for Solving the Problems

[0014] A first embodiment of the present invention is a lens assembling
method for assembling a first lens and a second lens where the first lens
has a first mark on a first surface thereof and a second mark on a second
surface opposite to the first surface, and the second lens has a third
mark on a first surface thereof, the lens assembling method including:

[0015] a first step of aligning a position of one of the first mark and
second marks of the first lens with a position of the third mark of the
second lens; and

[0016] a second step of aligning a position of the other one of the first
and second marks of the first lens with the position of the third mark of
the second lens, while keeping the position alignment performed in the
first step.

[0017] The second embodiment is the lens assembling method relating to the
first embodiment, wherein the second mark of the first lens and the third
mark of the second lens are provided so as to face each other, and

[0018] in the first step, the position of the second mark is aligned with
the position of the third mark.

[0019] A third embodiment of the present invention is a lens assembling
method for assembling a first lens and a second lens where the first lens
has a first mark on a first surface thereof and a second mark on a second
surface opposite to the first surface, and the second lens has a third
mark on a first surface thereof, the lens assembling method including:

[0020] a first step of aligning a position of one of the first mark and
second marks of the first lens with a position of the third mark of the
second lens; and

[0021] a second step of aligning a position of the other one of the first
and second marks of the first lens with the position of the third mark of
the second lens, while keeping the position alignment performed in the
first step,

[0022] wherein at least one of the first step and the second step is a
step of extrapolating a first virtual mark or a second virtual mark
respectively based on the first mark or the second mark, and aligning a
position of the first virtual mark or the second virtual mark with the
position of the third mark.

[0023] The fourth embodiment is the lens assembling method relating to the
third embodiment, wherein at least one of the first mark and the second
mark comprises multiple marks provided in an outer peripheral area on a
periphery of effective optical surface of the first lens, wherein

[0024] in the first step or the second step, with respect to the multiple
marks, a position of the virtual mark is extrapolated based on the
multiple marks provided in the outer peripheral area, and the position of
the virtual mark is aligned with the position of the third mark.

[0025] The fifth embodiment is the lens assembling method relating to the
fourth embodiment, wherein the multiple marks, provided in the outer
peripheral area, of the first or the second mark, are respectively
provided at a same distance from an optical axis of the first lens,
wherein

[0026] in the first step or the second step, with respect to the multiple
marks provided in the outer peripheral area, a weighted center position
of an area enclosed by the multiple marks is extrapolated as the virtual
mark, and the position of the virtual mark is aligned with the position
of the third mark.

[0027] The sixth embodiment is the lens assembling method relating to the
fourth or fifth embodiment, wherein positions of the multiple marks of
the first mark provided in the outer peripheral area, and positions of
the multiple marks of the second mark provided in the outer peripheral
area are arranged to be dislocated from each other.

[0028] The seventh embodiment is the lens assembling method relating to
the third embodiment, wherein at least one of the that mark and the
second mark is a circular mark centered with an optical axis of the first
lens, provided in an outer peripheral area on a periphery of effective
optical surface of the first lens, wherein

[0029] in the first step or the second step, with respect to the mark
provided in the outer peripheral area, a weighted center position of an
area enclosed by the circular mark is extrapolated as the virtual mark,
and the extrapolated position of the virtual mark is aligned with the
position of the third mark.

[0030] The eighth embodiment is the lens assembling method relating to the
seventh embodiment, wherein the circular mark of the first mark provided
in the outer peripheral area and the circular mark of the second mark
provided in the outer peripheral area have different diameters from each
other.

[0031] The ninth embodiment is the lens assembling method relating to any
of the first to second, or seventh embodiment, wherein the first or
second mark which is provided in the effective optical surface of the
first lens, is provided on the light axis of the first lens.

[0032] The tenth embodiment is the lens assembling method relating to any
of the first to ninth embodiments, wherein the third mark is provided on
the light axis of the second lens.

[0033] The eleventh embodiment is the lens assembling method relating to
any of the first to ninth embodiments, wherein the third mark comprises
multiple marks provided in an outer peripheral area on a periphery of
effective optical surface of the second lens, wherein

[0034] in the first step or the second step, a positions of a virtual
mark, with respect to the third mark, is extrapolated based on the
multiple marks of the third mark provided in the outer peripheral area,
and the position aligning is executed using the position of the virtual
mark as the position of the third mark.

[0035] The twelfth embodiment is the lens assembling method relating to
the eleventh embodiment, wherein the multiple marks of the third mark are
respectively arranged at positions of same distance from an optical axis
of the second lens, wherein

[0036] in the first step or the second step, a weighted center position of
an area enclosed by the multiple marks of the third mark is extrapolated
as a position of a virtual mark of the third mark, and the position
aligning is executed using the position of the virtual mark as the
position of the third mark.

[0037] The thirteenth embodiment is the lens assembling method relating to
any of the first to ninth embodiments, wherein the third mark is, a
circular mark centered with an optical axis of the second lens, provided
in an outer peripheral area on an periphery of an effective optical
surface of the second lens, wherein

[0038] in the first step or the second step, a weighted center position of
an area enclosed by the circular mark of the third mark is extrapolated
as a position of a virtual mark of the third mark, and the position
aligning is executed using the position of the virtual mark as the
position of the third mark.

[0039] The fourteenth embodiment is the lens assembling method relating to
the first or second embodiment, wherein the first mark and the second
mark are respectively provided on an optical axis of the first lens, and
the third mark is provided on an optical axis of the second lens.

[0040] The fifteenth embodiment is the lens assembling method relating to
any of the first to fourteenth embodiments, wherein sizes of the first
mark, second mark and the third mark are respectively different from each
other.

[0041] The sixteenth embodiment is a lens assembly including: a first lens
provided with a first mark on a first surface thereof, and a second mark
on a second surface opposite to the first surface; and

[0042] a second lens provided with a third mark, wherein

[0043] the lens assembly is assembled in conditions that a position of the
second mark and a position of the third mark are aligned to be matched
with each other, and a position of the first mark and the position of the
third mark are aligned to be matched with each other.

[0044] The seventeenth embodiment is the lens assembly relating to the
sixteenth embodiment, wherein the second lens is provided with a fourth
mark on an opposite side surface to the surface formed with the third
mark.

[0045] The eighteenth embodiment an image capturing device including:

[0046] the lens assembly described in claim 16 or claim 17; and

[0047] an image capturing sensor, which receives incident light having
passed through the first and second lenses, provided at an opposite
surface side, with respect to the second lens, to a surface side where
the first lens is arranged.

Effect of the Invention

[0048] According to the present invention, in the first step, the position
alignment of the first lens and the second lens can be performed in
parallel direction and, further in the second step, the adjustment of the
tilt between the lenses is enabled. In this way, the tilt between lenses
can be suppressed by the second step, as the result, production of a high
precision lens unit is enabled.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIGS. 1a-1c show a top view and section a view of a lens relating
to a first embodiment of the present invention.

[0050] FIGS. 2a-2c show lens section views illustrating an assembling
method of the lens relating to the first embodiment of the present
invention.

[0062] FIGS. 14a-14d show lens section views illustrating an assembling
method of the lens relating to a conventional method.

[0063]FIG. 15 shows a section view of a lens assembly relating to the
conventional method.

PREFERRED EMBODIMENT OF THE INVENTION

[0064] In the embodiment of the present invention, a plurality of lenses
is assembled, with respect to the lenses provided with marks, by
performing an axis alignment based on the marks. For example, in case of
assembling two lenses, marks are formed on both sides of at least one
lens, and a mark is formed on one side of the another lens. Then, by
performing the axis alignment by using these marks, the lenses are
assembled. By assembling the lenses with using these marks, lens
positioning in a parallel direction is conducted, and a tilt between the
lenses is further adjusted. A specific embodiment will be described
below.

First Embodiment

[0065] The lens and lens assembling method relating to the first
embodiment of the present invention will be described referring to FIGS.
1a2c. FIGS. 1a-1c show a top view and section a view of a lens relating
to the first embodiment of the present invention. FIGS. 2a-2c show lens
section views illustrating an assembling method of the lens relating to
the first embodiment of the present invention. FIG. 1a shows a top view
of a first lens 10 viewed from a side of one surface (first surface 11),
and a section view of the first lens 10 taken on a line passing a center
of the first lens. 10. FIG. 1b shows a top view of a second lens 20
viewed from a side of one surface (first surface 21), and a section view
of the second lens 20 taken on a center of the second lens 20. FIG. 1c
shows a section view of a lens assembly illustrating the assembled state
of the first lens 10 and the second lens 20.

[0066] As shown in FIGS. 1a-1c, the lens assembly relating to the first
embodiment is provided with the first lens 10 and the second lens 20. The
first lens has marks on both sides. For example, as shown in FIG. 1a,
with respect to the first lens 10, on one side surface (the first surface
11) at an optical axis of the lens, a first mark 12 shaped convex is
provided, and on the other side surface (the second surface 13), a second
mark 14 shaped convex is provided. Further, as shown in FIG. 1b, with
respect to the second lens 20, on one side surface (the first surface 21)
at an optical axis of the lens, a third mark 12 shaped convex is
provided. In this embodiment, on the second lens 20 at the optical axis
on a surface (the first surface 21) facing to the first lens 10, the
third mark 22 is provided. The first mark 12, the second mark 14, and the
third mark 22 have circular shapes view from the above direction as an
example. Then, as shown in FIG. 1c, by assembling the first lens 10 and
the second lens 20 so as to make the second surface 13 of the first lens
face the first surface 21 of the second lens 20, the lens assembly is
formed.

[0067] As an example, each diameter of the first lens 10 and the second
lens 20 is 3 mm, and a diameter of the first mark 12 or the like is not
greater than 50 μm. For example the diameter of the first lens 10 is
20 μm. The above sizes of the lens and the mark are only examples, and
the lens and the mark of the present invention are not restricted to
these sizes.

[0068] Although not illustrated in the drawings here, the image capturing
device is configured such that an image capturing sensor, to receive the
incident light passed through the first lens 10 and the second lens 20,
is arranged with a prescribed interval at the opposite surface side to
the first surface 21 of the second lens 20.

[0069] Shapes of first mark 12, the second mark 14, and the third mark 22
may be round in section view as shown in FIG. 1, or may be rectangular.
Further shapes of the first mark 12, the second mark 14, and the third
mark 22 may be convex shapes or may be concave shapes as grooves. Further
sizes of the first mark 12, the second mark 14, and the third mark 22 may
be the same or may be different from each other.

[0070] The first lens 10 and the second lens 20 may be made of resin or
may be made of glass.

(Lens Assembling Method)

[0071] Next, the assembling method of the first lens 10 and the second
lens 20 will be described referring to FIG. 2.

(First Process: Shift Alignment)

[0072] Firstly, as shown in FIG. 2a, by making the second surface 13 of
the first lens face to the first surface 21 of the second lens 20,
disposed is the first lens 10 above the second lens 20. Then matched is
the position of the third mark 22 provided on the second lens 20 to the
position of the second mark 14 provided on the first lens 10. For
example, by moving the first lens 10 in the parallel direction (X
direction) above the second lens 20, matched is the position of second
mark 14 to the position of the third mark 22.

[0073] Specifically, before placing the first lens 10 on the second lens
20, by observing the third mark 22 on the second lens 20 using a
microscope, measured is a position of the third mark 22 provided on the
second lens 20, for example, by using a three-dimensional coordinate
optical measuring machine (hereinafter referred as a coordinate measuring
machine). For measuring the three dimensional coordinate, a known
coordinate measuring machine can be used. The coordinate measuring
machine measures the coordinate of the third mark 22 by assuming, for
example, a previously determined position as a point of origin, and
retains the coordinate information.

[0074] Next, by making the second surface 13 face to the first surface 21
of the second lens 20, the first lens 10 is placed on the second lens 20.
Then, a position of the second mark 14 provided on the first lens 10 is
measured with the coordinate measuring machine, and the coordinate
information of the second mark 14 is retained. Thereafter, based on the
retained coordinate information, the first lens 10 is moved in parallel
direction (X direction) to match the position of the third mark 22 and
the position of the second mark 14 (shift alignment). And, by matching
the position of the second mark 14 provided on the first lens 10 and the
position of the third mark 22 provided on the second lens 20, the
positions of the first and second lenses are maintained.

(Second Process: Tilt Alignment)

[0075] Next, a position of the first mark 12 provided on the first surface
11 of the first lens 10 is measured with the coordinate measuring
machine, and the coordinate information of the first mark 12 is retained.
Then, with keeping the state that positions of the second mark 14 and the
third mark 22 are matched, the tilt of the first lens 10 is changed so as
to match the position of the first mark 12 and the position of the third
mark 22. For example, as shown in FIG. 2b, with keeping the state that
positions of the second mark 14 and the third mark 22 are matched, the
tilt of the first lens 10 is changed in θ direction so as to match
the position of the first mark 12 and the position of the third mark 22
(tilt alignment).

[0076] As described above, by matching the position of the first mark 12
and the position of the third mark 22 with keeping the state that the
positions of the second mark 14 and the third mark 22 are matched, the
tilt between the first lens 10 and the second lens 20 can be aligned.
Namely, according to this second process (tilt alignment), by adjusting
the tilt between the optical axis of the first lens 10 and the optical
axis of the second lens 20, suppressing of the tilt is enabled.

(Fixing the First Lens 10 and the Second Lens 20)

[0077] In the state that the position of the first mark 12 and the
position of the third mark 22 are matched, as shown in FIG. 2c, by
providing an adhesive 100 on the periphery of first lens 10 and second
lens 20, the first lens 10 and the second lens 20 are adhesively fixed.

[0078] As described above, according to the first process (shift
alignment), matching the position of first lens 10 and the position of
second lens 20 is enabled. Further, according to the second process (tilt
alignment) the suppression of the tilt of optical axes is enabled by
adjusting the tilt between the first lens 10 and the second lens 20.

[0079] As described above, according to the lens assembling method
relating to the present embodiment, by measuring and aligning the first
mark 12, second mark 14 and the third mark 22, a relative tilt (relative
tilt amount), which cannot be detected by the conventional method, is
enabled to be measured and aligned. Accordingly, it is enabled to
suppress the relative tilt between lenses and to easily produce a high
precision lens unit.

[0080] For example in the conventional technology shown in FIG. 15, tilts
of 5' (5 arc-minutes) to 10' between lenses are generated. In contrast,
according to the assembling method relating to the present embodiment, it
is enabled to suppress the tilt between the first lens 10 and the second
lens to 2' or less. For a high pixel optical system of 12 million pixels
class, the tilt between lenses is required to be 3' or less. According to
the assembling method relating to the present embodiment, since the tilt
between lenses can be suppressed to 2' or less, the tilt amount required
for the high pixel optical system can be satisfied.

[0081] In the above description, the configuration is explained where the
third mark 22 provided on the second lens 20 faces the second mark 14
provided on the first lens 10. This is because visibility of the mark is
higher when the mark is nearer, since the positioning is conducted by
viewing the mark through the first lens 10. However, the present
invention is not restricted to this. Namely the third mark 22 provided on
the second lens 20 may be located on an opposite surface to the surface
facing to the mark provided on the first lens 10, and the shift alignment
may be performed between the marks that do not face with each other.

(Other Examples of the Mark)

[0082] The other example of the marks provided on the first lens 10 and
the second lens 20 is shown in FIG. 3. FIG. 3 is a top view showing
another example of the mark. For example the first mark 12A is X shaped
when viewing from above. Namely the first mark 12A has a shape of crossed
two line segments. Like this, the figure of the marks provided on the
first lens 10 and the second lens 20 may be X shaped.

[0083] The X shaped mark may be convex mark or concave mark having a
grooved shape. Each of the marks provided on the first lens 10 and the
second lens 20 may have a same figure or different figure with each
other. Further said each mark may have a same size or respective
different size.

[0084] Further, the size and figure of each mark is preferably varied with
each other. By this, since each mark can be easily identified and
detected, easy lens assembly is enabled.

[0085] Further, from the view point that the metal mold for molding the
first lens 10 and the second lens 20 is manufactured by processing the
material while rotating it, each mark is preferably has a rounded figure.

VARIANT EXAMPLE 1

[0086] Next, the lens relating to variant example 1 is described referring
to FIGS. 4a and 4b. FIGS. 4a-4b show section views of the lens relating
to variant example 1. Although, in the above described first embodiment,
marks are provided on both surfaces of the first lens 10 and another mark
is provided on one side surface of the second lens 20, marks may be
provided on both sides of each of the lenses. For example, regarding the
second lens 20, as shown in FIG. 4a, the third mark 22 is provided at an
optical axis of the lens on one side surface (the first surface 21), and
the fourth mark 24 is provided at an optical axis of the lens on the
other side surface (the second surface 23). In this way, the marks (the
first mark 12, the second mark 14) are provided on both surfaces of the
first lens 10 and the marks (the third mark 22, the fourth mark 24) are
provided on both surfaces of the second lens 20. According to this, the
more precise alignment is enabled. The lenses relating to the variant
example 1 can be also assembled by the same assembling method of the
above described embodiment 1. Namely, according to the first process
(shift alignment), the position of first lens 10 and the position of
second lens 20 is matched in the parallel direction, further, according
to the second process (tilt alignment) the tilt of optical axes between
the first lens 10 and the second lens 20 is adjusted. By this assembling
method, the relative tilt between the lenses is suppressed and an easy
production of a high precision lens unit is enabled.

[0087] Namely by providing the marks on both surfaces of the first lens
10, and further providing the marks on both surfaces of the second lens
20, the optical axis of the second lens 20 can be precisely measured, and
the optical axes of the first lens 10 and the second lens 20 can be
aligned in parallel. Accordingly, production of a higher precision lens
unit is enabled than the case of providing the mark on only one side
surface of the second lens 20.

[0088] Further, as shown in FIG. 4b, in the second lens 20, the fourth
mark 24 is provided at the optical axis on the second surface 23, and any
mark may not be provided on the first surface. Namely, by the first
process (shift alignment), the position of the fourth mark 24 provided on
the second lens 20 and the position of the second mark 14 provided on the
first lens 10 is matched. Due to this, the position between the first
lens 10 and the second lens 20 is aligned in the parallel direction.
Further, according to the second process (tilt alignment) the position of
the first mark 12 and the fourth mark 24 are matched while keeping the
matched state between the position of the second mark 14 and the position
of the fourth mark 24. By this, the tilt between the first lens 10 and
the second lens 20 is adjusted. By this assembling method, the relative
tilt between the lenses is suppressed and an easy production of a high
precision lens unit is enabled.

[0089] As described above, in this embodiment, by forming marks on both
surfaces of at least one lens out of the two lenses, and forming a mark
on one side surface of the another lens, the relative tilt between the
lenses is suppressed and an easy production of a high precision lens unit
is enabled.

VARIANT EXAMPLE 2

[0090] Next, lenses relating to variant example 2 are described referring
to FIGS. 5a and 5b. FIGS. 5a-5b show section views of the lenses relating
to variant example 2. In case of assembling a plurality of lenses, a lens
frame may be used. For example, as shown in FIG. 5a, assembling may be
conducted by holding side surfaces of the first lens 10 and the second
lens 30 with a lens frame 520 to fix the positions of the first lens 10
and the second lens 30. In the variant example 2, marks are provided on
both surfaced of the second lens 30. The first mark 31 is provided at the
optical axis on the surface facing the first lens 10. The second mark 32
of the second lens 30 is provided at the optical axis of said lens on the
opposite side surface to the first surface. Even in cases of assembling
the lenses using the lens frame 520, similarly to the above described
first embodiment, assembling is enabled by adjusting the tilt between the
first lens 10 and the second lens 30. As the result, suppression of the
relative tilt between the lenses is enabled. Further, even in cases where
the first lens 10 provided with marks on both surfaces and the second
lens 20 provided with the mark on one side surface are assembled, the
lens frame 520 may be utilized.

[0091] Further, as shown in FIG. 5b, even in cases of assembling a lens
unit and a diaphragm 600, the sift alignment and the tilt alignment can
be executed by utilizing the two marks (the first mark 12 and the second
mark 14) provided on the first lens 10. Namely, by matching the positions
of the first mark 12 and the second mark 14 with respect to a center of
opening section 610 provided on the diaphragm 600, the shift alignment
and the tilt alignment can be executed. As the result, easy production of
a high precision lens unit is enabled. Further, even after assembling of
the lens unit, a position measurement of the diaphragm 600 and the
optical axis of lens unit can be easily executed.

Second Embodiment

[0092] Next, the lens and lens assembling method relating to the second
embodiment of the present invention will be described referring to FIGS.
6a-6c. FIGS. 61a-6c show a top view and a section view of a lens relating
to the second embodiment of the present invention. FIG. 6a shows a top
view of a first lens 40 viewed from a side of one surface (the surface
including an effective optical surface 41a), and a section view of the
first lens 40 taken on a line passing a center of the first lens 40. FIG.
6b shows a top view of a second lens 20 viewed from a side of one surface
(first surface 21), and a section view of the second lens 20 taken on a
line passing a center of the second lens 20. FIG. 6c shows a section view
of a lens assembly illustrating the assembled state of the first lens 40
and the second lens 20.

[0093] In the above described first embodiment, a mark is provided on the
optical axis of the lens. On the other hand, in the second embodiment,
the mark is provided at the other position than the optical axis. For
example, the mark is provided in an outer peripheral area on the
periphery of the effective optical surface of the lens.

[0094] Specifically, as shown in FIG. 6a, the first lens 40 is provided
with marks on both side surfaces. The first surface of the first lens 40
is configured with effective optical surface 41a including the optical
axis, and an outer peripheral area 41b existing in a periphery of the
effective optical surface 41a. The second surface opposite to the first
surface is configured with effective optical surface 44a including the
optical axis, and an outer peripheral area 44b existing in a periphery of
the effective optical surface 44a. On the outer peripheral area 41b of
the first surface, three marks (first marks 42a, 42b, and 42C) are
provided by centering the optical axis with respective intervals of the
same angle from each other. For example, the first marks 42a, 42b, and
42c are provided by centering the optical axis with respective intervals
of 120 degrees, on the outer peripheral area 41b. Further, the first
marks 42a, 42b, and 42c are respectively provided at the same distance
from the optical axis. Namely, on a same circle centering the optical
axis, the first marks 42a, 42b, and 42c (hereinafter may be referred as
first mark 42 etc.) are respectively provided. Further, on the second
surface, second mark 45 is provided on the optical axis in the effective
optical surface 44a. Further, as shown in FIG. 6b, in the second lens 20,
third mark 22 is provided on the optical axis in one side surface (first
surface 21).

[0095] Similarly to the first embodiment, the first mark 42 etc., the
second mark 45 and the third mark 22 may have a circular form, or a
rectangular form. Further a shape of the first mark 12, the second mark
14, and the third mark 22 may be concave form or convex form as a groove.
Further sizes of these marks may be the same or may be different from
each other.

[0096] Then, as shown in FIG. 6c, by making the second surface (including
the effective optical surface 44a) of the first lens and the first
surface 21 of the second lens face with each other, and combining the
first lens 40 and the second lens 20, the lens assembly is formed.

(Lens Assembling Method)

[0097] Next, the method of combining the first lens 40 and the second lens
20 will be described. Firstly, similarly to the first embodiment, by
making the second surface (the surface including the effective optical
surface 44a) of the first lens 40 face to the first surface 21 of the
second lens 20, the first lens 40 is disposed above the second lens 20.
Then the position of the third mark 22, provided on the second lens 20,
is matched to the position of the second mark 45 provided on the first
lens 40. To be more specific, similarly to the first embodiment, by
measuring the position of the second mark 45 and the position of the
third mark 22 with a coordinate measuring machine, the first lens 40 is
moved in parallel direction (shift alignment) so that the position of the
third mark 22 and the position of the second mark 45 match with each
other, based on coordinate information of each mark. And the positions of
the first lens 40 and the position of the second lens 20 are maintained
with the condition that the position of the second mark 45 and the
position of the third mark 22 are matched.

[0098] Next, by measuring with the coordinate measuring machine the
positions of the first marks 42a, 42b and 42c, the coordinate information
of the first marks 42a, 42b and 42c is retained. Then, based on each
coordinate information of the first marks 42a, 42b and 42c, the weighted
center position of the area enclosed by the first marks 42a, 42b and 42c
is extrapolated. For example, the weighted center position of a triangle
formed by the first marks 42a, 42b and 42c is extrapolated. Since the
first mark 42a, etc. are provided at an equal distance from the optical
axis, the extrapolated weighted center is to be positioned on the optical
axis of the first lens 40. That is to say, since the third mark 22 of the
second lens 20 is provided on the optical axis, the first mark 42a, etc.
are provided in the outer peripheral area 41b of the first lens 40 so
that the extrapolated weighted center position is located on the optical
axis of the first lens 40. For example, as shown in FIG. 6a, by
specifying the weighted center position based on the first mark 42a,
etc., the weighted center position is defined as the position of virtual
mark 43. Since the weighted center position extrapolated by the first
marks 42a, etc. is positioned on the optical axis of the first lens 40,
the virtual mark 43 is also positioned on the optical axis of the first
lens 40. In the second embodiment, although three marks are provided in
the outer peripheral area, four or more marks may be provided in the
outer peripheral area to extrapolate the virtual mark.

[0099] Said weighted center position is at the same position as the center
position of the plane figure.

[0100] Then, while keeping the state that the position of the second mark
45 is matched to the position of the third mark 22, changed is the tilt
of first lens 40 so that the position of virtual mark 43 on the first
lens 40 is matched to the position of the third mark 22 (tilt alignment).
In this way, by matching the position of virtual mark 43 and the position
of third mark 22 in the state that the position of the second mark 45 is
matched to the position of the third mark 22, the tilt between the first
lens 40 and the second lens 20 can be aligned. As the result, by
adjusting the tilt between the optical axis of first lens 40 and the
optical axis of second lens 20, this tilt is enabled to be suppressed.

[0101] As described above, even in cases where the mark is formed at a
position other than the optical axis, by forming marks on both side
surfaces of one lens, a high precision lens unit is enabled to be easily
produced with suppressed relative tilt between lenses.

[0102] Further, in the first lens 40, the second mark 45 is provided at
the optical axis on one side surface (the surface including the effective
optical surface 44a), and the first mark 42a is provided in the outer
peripheral area 41b other than the optical axis. In this way, by
providing the marks at displaced positions on each surface, mark
positions on both surfaces are not overlapped with each other, and the
position of each mark is enabled to be measured in high precision.

(Another Example of Mark)

[0103] Another example of the mark provided on the first lens 40 is shown
in FIG. 7. FIG. 7 is a top view illustrating another example of the mark.
For example, the first mark 46a, 46b, and 46c has an X shaped figure
viewing from above. Namely, the first mark 46a etc. has a figure of
crossed two lines. As this, the figure of the mark provided on the outer
peripheral area 41b of the first lens 40 may be the X shaped figure.
Further, the second mark 45 provided on the first lens 40 may be X
shaped, and the third mark 22 provided on the second lens 20 may be X
shaped.

VARIANT EXAMPLE 3

[0104] Next, the lens relating to variant example 3 is described referring
to FIGS. 8a-8c. FIGS. 8a-8c show top views and section views of the lens
relating to variant example 3. In the above described second embodiment,
the second mark 45 is provided at the optical axis on the second surface
facing to the second lens 20, and the first mark 42a etc. is provided in
the peripheral area 41b on the first surface (the surface including the
effective optical surface 41a) opposite to the second surface. As this
variant example, the first mark may be provided at the optical axis on
the first surface of said lens, and a plurality of the second marks may
be provided in the outer peripheral area of the second surface.

[0105] As shown in FIG. 8a for example, the first surface of the first
lens 60 is configured with effective optical surface 61a including an
optical axis and outer peripheral area 61b existing in the periphery of
the effective optical surface 61a. And, the second surface, which is on
opposite side to the first surface, is configured with effective optical
surface 63a including an optical axis and outer peripheral area 63b
existing in the periphery of the effective optical surface 63a. On the
first surface, the first mark 62 is provided at the center of the
effective optical surface 61a. On the outer peripheral area 63b of the
second surface, three marks (second marks 64a, 64b, and 64c) are provided
by centering the optical axis with respective intervals of the same angle
from each other. For example, the second marks 64a, 64b, and 64c are
provided by centering the optical axis with respective intervals of 120
degrees in the outer peripheral area 63b. Further, the second marks 64a,
64b, and 64c are respectively provided at the same distance from the
optical axis. Namely, on a same circle centering the optical axis, the
second marks 64a, 64b, and 64c (hereinafter may be referred as second
mark 64a etc.) are respectively provided. Further, as shown in FIG. 8b,
in the second lens 20, third mark 22 is provided on the optical axis in
one side surface (first surface 21).

[0106] Then, as shown in FIG. 8c, by making the second surface (including
the effective optical surface 63a) of the first lens and the first
surface 21 of the second lens face with each other, and combining the
first lens 60 and the second lens 20, the lens assembly is formed.

(Lens Assembling Method)

[0107] Lenses relating to the third variant example can be assembled
similarly to the lenses relating to the second embodiment. First,
measuring the position of the third mark 22 provided on the second lens,
and the coordinates of the third mark is retained. Then by disposing the
first lens 60 above the second lens, and measuring with the coordinate
measuring machine the positions of the second marks 64a, 64b and 64c
provided in the outer peripheral area 63a of the first lens 60, the
coordinates of the second mark 64a, 64b and 64c is retained. Next, based
on each piece of coordinate information of the second marks 64a, 64b and
64c, the weighted center position of the area enclosed by the second
marks 64a, 64b and 64c is extrapolated. For example, the weighted center
position of a triangle formed by the second marks 64a, 64b and 64c is
extrapolated. Since the second marks 64a, 64b and 64c are provided at an
equal distance from the optical axis, the extrapolated weighted center is
to be positioned on the optical axis of the first lens 60. The weighted
center position is defined as the position of virtual mark.

[0108] Then, the position of the third mark provided on the second lens 20
and the extrapolated position to the virtual mark are matched with each
other. To be more specific, the first lens 60 is moved in parallel
direction (shift alignment) so that the position of the third mark 22 and
the position of the virtual mark match with each other. And the positions
of the first lens 60 and the position of the second lens 20 are
maintained with the condition that the position of the third mark 22 and
the position of the virtual mark are matched.

[0109] Next, by measuring the position of the first mark provided on the
first surface (the surface including the effective optical surface 61a)
of the first lens 60 with the coordinate measuring machine, the
coordinate information of the first mark 62 is retained. Then, while
keeping the state that the position of the virtual mark is matched to the
position of the third mark 22, the tilt of first lens 60 is changed so
that the position of the first mark 62 is matched to the position of the
third mark 22 (tilt alignment). In this way, by matching the position of
first mark 62 and the position of third mark 22 in the state that the
position of the virtual mark is matched to the position of the third mark
22, the tilt between the first lens 60 and the second lens 20 can be
aligned. As the result, by adjusting the tilt between the optical axis of
first lens 60 and the optical axis of second lens 20, said tilt is
enabled to be suppressed.

VARIANT EXAMPLE 4

[0110] Next, the lens relating to variant example 4 is described referring
to FIGS. 9a-9c. FIGS. 9a-9c show top views and section views of the lens
relating to variant example 4. In the above described second embodiment
and the variant example 3, the mark is provided in the outer peripheral
area of the one lens. As a variant example to these, marks may be
provided in outer peripheral arias on two lenses.

[0111] As shown in FIG. 9a for example, the first surface of the first
lens 70 is configured with effective optical surface 71a including an
optical axis and outer peripheral area 71b existing in the periphery of
the effective optical surface 71a. And, the second surface, which is on
opposite side to the first surface, is configured with effective optical
surface 74a and outer peripheral area 74b existing in the periphery of
the effective optical surface 74a. On the outer peripheral area 71b of
the first surface, three marks (first marks 72a, 72b, and 72c) are
provided by centering the optical axis with respective intervals of the
same angle. For example, the first marks 72a, 72b, and 72c are provided
by centering the optical axis with respective intervals of 120 degrees
from each other. Further, the first marks 72a, 72b, and 72c are
respectively provided at the same distance from the optical axis. Namely,
on a same circle centering the optical axis, the first marks 72a, 72b,
and 72c (hereinafter may be referred as first marks 72a etc.) are
respectively provided,

[0112] Further, also on the outer peripheral area 74b of the second
surface, three marks (second marks 75a, 75b, and 75c) are provided by
centering the optical axis with respective intervals of the same angle.
For example, the second marks 75a, 75b, and 75c are provided by centering
the optical axis with respective intervals of 120 degrees. Further, the
second marks 75a, 75b, and 75c are respectively provided at the same
distance from the optical axis. Namely, on a same circle centering the
optical axis, the second marks 75a, 75b, and 75c (hereinafter may be
referred as second marks 75a etc.) are respectively provided.

[0113] Wherein, it is preferable to provide the first marks 72a etc., and
the second marks 75a etc., on the first lens 70 by relatively displacing
the angle with each other. Namely, although each of the first marks 72a
etc. and the second marks 75a etc. are respectively provided on the first
lens 70 with the interval of 120 degrees, it is preferable to provide the
first marks 72a etc., and the second marks 75a etc., with displacing the
phase from each other. In this way, by providing the first marks 72a
etc., and the second marks 75a etc., with displacing the phase from each
other, mark positions on both surfaces are not overlapped with each
other, and the position of each mark is enabled to be measured in high
precision. Further each of the marks may be provided on the first lens 70
by shifting the diameter of the circle passing through the first marks
72a etc., from the diameter of the circle passing through the second
marks 75a etc. For example, by providing the second marks 75a etc., at
inside or outside of the first marks 72a etc., the positions of the first
marks 72a etc., and the second marks 75a etc., are displaced from each
other, and high precision measurement of the position of each mark is
enabled.

[0114] Further, as shown in FIG. 9b, the first surface of the second lens
80 (the surface opposing to the first lens 70) is configured with
effective optical surface 81a including an optical axis and outer
peripheral area 81b existing in the periphery of the effective optical
surface 81a. In the outer peripheral area 81b in the first surface, three
marks (third marks 82a, 82b, and 82c) are provided by centering the
optical axis with respective intervals of the same angle. For example,
the third marks 82a, 82b, and 82c are provided by centering the optical
axis with respective intervals of 120 degrees. Further, the third marks
82a, 82b, and 82c are respectively provided at the same distance from the
optical axis. Namely, on a same circle centering the optical axis, the
third marks 82a, 82b, and 82c (hereinafter may be referred as third marks
82a etc.) are respectively provided.

[0115] Then, as shown in FIG. 9c, by making the second surface (including
the effective optical surface 74a) of the first lens 70 and the first
surface (including the effective optical surface 81a) of the second lens
80 face with each other, and combining the first lens 70 and the second
lens 80, the lens assembly is formed.

(Lens Assembling Method)

[0116] Lenses relating to the fourth variant example can be assembled
similarly to the lenses relating to the second embodiment. First,
measuring with the coordinate measuring machine the position of the third
marks 82a, 82b, and 82c provided in the outer peripheral area 81b of the
second lens, and the coordinates of the third marks 82a, 82b, and 82c is
retained. Next, based on respective coordinate information of the third
marks 82a, 82b, and 82c, the weighted center position of the area
enclosed by the third marks 82a, 82b, and 82c is extrapolated. For
example, the weighted center position of a triangle formed by the third
marks 82a, 82b, and 82c is extrapolated. Since the third marks 82a, 82b,
and 82c are provided at an equal distance from the optical axis, the
extrapolated weighted center is to be positioned on the optical axis of
the second lens 60. For example, as shown in FIG. 9b, by specifying the
position of the weighted center based on the third marks 82a, etc, the
weighted center position is defined as the position of the third virtual
mark 83.

[0117] Then by disposing the first lens 70 above the second lens 80, and
measuring with the coordinate measuring machine the position of the
second marks 75a, 75b, and 75c provided in the outer peripheral area 74b
of the first lens 70, and the coordinates of the second marks 75a, 75b,
and 75c is retained. Next, based on respective coordinate information of
the second marks 75a, 75b, and 75c, the weighted center position of the
area enclosed by the second marks 75a, 75b, and 75c is extrapolated. For
example, the weighted center position of a triangle formed by the second
marks 75a, 75b, and 75c is extrapolated. Since the second marks 75a, 75b,
and 75c are provided at an equal distance from the optical axis, the
extrapolated weighted center is to be positioned on the optical axis of
the first lens 70. The weighted center position is defined as the
position of the second virtual mark.

[0118] Then, the position of the third virtual mark 83 extrapolated in the
second lens 80 and the position of the extrapolated second virtual mark
in the first lens 70 are matched with each other. To be more specific,
the first lens 70 is moved in parallel direction (shift alignment) so
that the position of the second virtual mark and the position of the
third virtual mark 83 match with each other. And the position of the
first lens 70 and the position of the second lens 80 are maintained with
the condition that the position of the second virtual mark and the
position of the third virtual mark 83 are matched with each other.

[0119] Then, by measuring with the coordinate measuring machine the
position of the first marks 72a, 72b, and 72c provided on the first
surface (the surface including the effective optical surface 71a) of the
first lens 70, the coordinate information of the first marks 72a, 72b,
and 72c is retained. Next, based on respective coordinate information of
the first marks 72a, 72b, and 72c, the weighted center position of the
area enclosed by the first marks 72a, 72b, and 72c is extrapolated. For
example, the weighted center position of a triangle formed by the first
marks 72a, 72b, and 72c is extrapolated. Since the first marks 72a, 72b,
and 72c are provided at an equal distance from the optical axis, the
extrapolated weighted center is to be positioned on the optical axis of
the first lens 70. For example, as shown in FIG. 9a, by specifying the
position of the weighted center based on the first marks 72a, etc, the
weighted center position is defined as the position of the first virtual
mark 73.

[0120] Then, while keeping the state that the position of the second
virtual mark is matched to the position of the third virtual mark, the
tilt of first lens 70 is changed so that the position of the first
virtual mark 73 is matched to the position of the third virtual mark 83
(tilt alignment). In this way, by matching the position of the first
virtual mark 73 and the position of the third virtual mark 83 in the
state that the position of the second virtual mark is matched to the
position of the third virtual mark 83, the tilt between the first lens 70
and the second lens 80 can be aligned. As the result, by adjusting the
tilt between the optical axis of first lens 70 and the optical axis of
second lens 80, said tilt is enabled to be suppressed.

(Another Example of Mark)

[0121] Another example of the mark provided on the outer peripheral area
of lens is shown in FIG. 10. FIG. 10 is a top view and a section view
illustrating another example of the mark. For example, the first surface
of the first lens 90 is configured with effective optical surface 91a
including an optical axis and outer peripheral area 91b existing in the
periphery of the effective optical surface 91a. In this outer peripheral
area 91b of the first surface, provided is first mark 92 figured of
convex concentric ring centered by an optical axis. Further, on second
surface 93 opposite to the first surface, second mark 94 is provided at
the optical axis. In the case where the concentric first mark 92 is
provided in the outer peripheral area 91b, similarly to the above
described second embodiment, the position of the first mark is also
measured. Then, by extrapolating the position of the weighted center of
the area enclosed by the first mark 92 based on the position of the first
mark 92, the extrapolated position of the weighted center is defined as
the position of virtual mark. In the example shown in FIG. 10, since the
first mark 92 is a circle shaped mark centered by the optical axis, the
position of the weighted center coincides with the position of the
optical axis. In the case of assembling the fast lens 90 and the second
lens (unillustrated), position alignment of the mark is executed with the
reference of the extrapolated weighted center position. In this way, even
in cases where the figure of mark provided in the outer peripheral area
is made to be concentric, the relative tilt between the lenses is
suppressed, and a high precision lens unit is enabled to be easily
produced.

[0122] Although figure of the first mark 92 is rectangle in cross section,
the cross section may be figured with curved lines. For example, the
cross section of the first mark 92 may be a figure which becomes
gradually narrower toward a tip. Further, although the first mark 92 is
convex in cross section, a concentric circled groove mark may be provided
in the outer peripheral area 91b.

[0123] Further, concentric circular marks may be provided in outer
peripheral areas on both side surfaces of the first lens 90. In this case
it is preferable to vary the diameter of the concentric circular mark
provided on the first surface from the diameter of the concentric
circular mark provided on the second surface. By varying each diameter of
the concentric circular marks provided on both sides, the mark positions
do not overlap in both sides, which enable to measure the position of
each mark in high precision. Further, in the second lens to be combined
with the first lens 90, the concentric circular mark may be provided in
the outer peripheral area of effective optical surface.

[0124] Further, from the view point of making a mold for molding lenses,
the figure of the mark to be provided in the outer peripheral area of the
lens is preferably be concentric circle. Namely, from the view point of
processing the mold, forming the mark of concentric circle is easier than
forming a plurality of marks to be positioned on a same circle, in the
outer peripheral area of the mold.

[0125] In cases of forming a lens by resin molding, contraction is larger
in the periphery area than in the central area of the lens. Therefore, is
more preferable to form the mark on an optical axis of the lens, as the
lens relating to the first embodiment, than to form the mark in the outer
peripheral area of the lens.

Third Embodiment

[0126] Next, lenses relating to the third embodiment of the present
invention will be described referring to FIG. 11. FIG. 11 show a section
view of the lenses relating to the third embodiment of the present
invention. Although in the above described embodiments two lenses are
combined, three or more lenses may be combined. For example, even in the
case of combining first lens 10, second lens 20 and third lens 30, by
repeating the assembling method relating to the above described
embodiments, the tilt between the lenses can be suppressed to enable the
production of high precision lens unit.

[0127] Each of the first lens 10 and the second lens 20 has marks on both
surfaces similarly to the lens assembly shown in FIGS. 4a-4b. In the
third lens 110, on the optical axis of the first surface 111 facing to
the second lens 20, convex shaped fifth mark 112 is provided.

(Lens Assembling Method)

[0128] Assembling method of three lenses will be described. First,
measuring with the coordinate measuring machine the position of the fifth
mark 112 provided on the third lens 110, and the coordinates of the fifth
mark 112 is retained. Next, the second lens 20 is disposed above the
third lens 110 by making the second surface 23 of the second lens 20 face
to the first surface 111 of the third lens 110. And, by measuring with
the coordinate measuring machine the position of the fourth mark 24
provided on the second surface 23 of the second lens 20, the coordinates
of fourth mark 24 is retained. Next, based on the retained coordinate
information, the second lens 20 is moved in parallel direction so that
the position of the fifth mark 112 and the position of the fourth mark 24
match with each other (shift alignment). Then, by matching the position
of the fourth mark 24 provided on the second lens 20 with the position of
the fifth mark 112 provided on the third lens 110, the position of the
second lens 20 and the position of the third lens 110 are maintained with
the matched state.

[0129] Next, by measuring with the coordinate measuring machine the
position of the third mark 22 provided on the first surface 21 of the
second lens 20, the coordinates of the third mark 22 is retained. Then,
while keeping the state that the position of the fourth mark 24 and the
position of the fifth mark 112 are matched, tilt of the second lens 20 is
changed so that the position of the third mark 22 and the position of the
fifth mark 112 match with each other (tilt alignment). As the result, by
adjusting the tilt between the optical axes of second lens 20 and the
third lens 110, the tilt is enabled to be suppressed.

[0130] Next, the first lens 10 is disposed above the second lens 20 by
making the second surface 13 of the first lens 10 face to the first
surface 21 of the second lens 20. And, by measuring with the coordinate
measuring machine the position of the second mark 14 provided on the
second surface 13 of the first lens 10 and the coordinates of second mark
14 is retained. Next, based on the retained coordinate information, the
first lens 10 is moved in parallel direction so that the position of the
third mark 22 and the position of the second mark 14 match with each
other (shift alignment). Then, by matching the position of the second
mark 14 provided on the first lens 10 with the position of the third mark
22 provided on the second lens 20, the position of the first lens 10 and
the position of the second lens 20 are maintained with the matched state.

[0131] Next, by measuring with the coordinate measuring machine the
position of the first mark 12 provided on the first surface 11 of the
first lens 10, the coordinates of the first mark 12 is retained. Then,
while keeping the state that the position of the second mark 14 and the
position of the third mark 22 are matched, tilt of the first lens 10 is
changed so that the position of the first mark 12 and the position of the
third mark 22 match with each other (tilt alignment). As the result, by
adjusting the tilt between the optical axes of the first lens 10 and the
second lens 20, the tilt is enabled to be suppressed.

[0132] As described above, even in the case of assembling three or more
lenses, by repeating the shift alignment and the tilt alignment, the tilt
between the lenses can be suppressed to enable the production of high
precision lens unit.

[0133] In the third embodiment, although the mark is provided on the
optical axis of each lens, a plurality of marks or a concentric circular
mark may be provided in an effective optical surface of each lens for
executing the alignment.

VARIANT EXAMPLE 5

[0134] Next, the lens relating to variant example 5 is described referring
to FIG. 12. FIG. 12 shows a section view of the lenses relating to
variant example 5. In the above described lens assembly relating to the
third embodiment, the marks are provided on both side surfaces of the
second lens 20 provided between the first lens 10 and the third lens 110.
As the variant example, the mark is not necessarily provided on the
second lens 20.

[0135] As shown in FIG. 12 for example, the first lens 10 is provided with
marks on both side surfaces, and the third lens 110 is provided with a
mark on one side. While, the second lens 20 is not provided with any
mark. In this case, since the second lens 20 is not required of very high
accuracy position alignment, the shift alignment and the tilt alignment
are executed with respect to the first lens 10 and the third lens 110,
after disposing the second lens 20 on the third lens 110. Namely, the
first lens 10 is moved in parallel direction so that the position of the
fifth mark 112 provided on the third lens 110 and the position of the
second mark 14 provided on the second surface 13 of the first lens 10
match with each other (shift alignment). Then, while keeping the state
that the position of the second mark 14 and the position of the fifth
mark 112 are matched, tilt of the first lens 10 is adjusted so that the
position of the first mark 12 provided on the first surface 11 of the
first lens 10 and the position of the fifth mark 112 match with each
other (tilt alignment). As the result, by executing the shift alignment
and the tilt alignment with respect to the first lens 10 and the third
lens 110, the tilt between the first lens 10 and the third lens 110 is
enabled to be suppressed.

VARIANT EXAMPLE 6

[0136] Next, the lens relating to variant example 6 is described referring
to FIG. 13. FIG. 13 shows a section view of the lenses relating to
variant example 6. As the variant example relating to the lens assembly
relating to the third embodiment, the third mark 22 may be provided only
on the first surface 21 of the second lens 20.

[0137] As shown in FIG. 13 for example, the first lens 10 is provided with
marks on both side surfaces, the second lens 20 is provided with a mark
on the first surface 21, and the third lens 110 is provided with the
fifth mark 112 on the first surface 111. In this case, after disposing
the second lens 20 on the third lens 110, the second lens 20 is moved in
parallel direction so that the position of the fifth mark 112 provided on
the third lens 110 and the position of the third mark 22 provided on the
second lens 20 match with each other (shift alignment). Next, the first
lens 10 is moved in parallel direction so that the position of the fifth
mark 112 provided on the third lens 110 and the position of the second
mark 14 provided on the second surface 13 of the first lens 10 match with
each other (shift alignment). Then, while keeping the state that the
position of the second mark 14 and the position of the fifth mark 112 are
matched, the tilt of the first lens 10 is adjusted so that the position
of the first mark 12 provided on the first 11 of the first lens 10 and
the position of the fifth mark 112 match with each other (tilt
alignment). In this way, the tilt between the first lens 10 and the third
lens 110 is enabled to be suppressed.

[0138] As described above, even in cases of assembling three or more
lenses, by executing the alignment with providing marks on both sides of
any one lens, the tilt between lenses can be suppressed to enable the
production of high precision lens units.